Indexable cutting insert for rotary cutting tools

ABSTRACT

A cutting insert having helically arranged teeth, each comprising a six sided block having two major parallel rhomboid-shaped plane surfaces constituting a seating face and a clearance face respectively, two opposed minor side surfaces constituting cutting faces extending between the seating and clearance faces, each cutting face forming an acute angle with the clearance face and forming a cutting edge along the intersection therewith, and two minor parallel plane end faces extending between the seating face and the two cutting faces. Each cutting face has a concave curvature located centrally of its major dimension, and a convex curvature at each end of its major dimension to define a serpentine cutting face and cutting edge. When disposed along the helically arranged teeth of a rotary cutting tool, such as a milling cutter, the inserts form a cutting face, or a radial face, having a continuously variable positive radial rake angle, and a cutting edge of serpentine configuration which generally parallels the helical form of the teeth.

BACKGROUND OF THE INVENTION

This invention relates to cutting inserts for rotary cutting tools, and,more particularly, indexable cutting inserts for rotary cutting toolssuch as milling cutters having helically arranged teeth.

For illustrative purposes, this specification will describe theinvention as it pertains to a conventional milling cutter,. i.e., amilling cutter having a shank portion and a cutting portion ofcylindrical configuration, the cutting portion containing a plurality ofhelically disposed gullets extending from the shank end of the cuttingportion to the free end thereof, which gullets define a plurality ofhelically arranged teeth. In such a milling cutter, the cutting edges,which comprise the leading edges of the teeth defined by the gullets,lie on a substantially constant radius with respect to the longitudinalaxis of the tool, throughout the length of the cutting portion. However,the invention may have application to other types of milling cutters,and other types of cutting tools which have helically arranged teeth andwhich utilize replaceable cutting inserts.

In a conventional rotary cutting tool wherein the teeth and cuttingedges are integral with the tool body, the cutting edges of the teethmay be sharpened, within defined limits. However, generally speakingwhen the cutting edges become worn or damaged beyond restoration, theentire tool must be discarded, and, as such tools conventionallycomprise very expensive high performance cutting steels, the replacementof such tools entails considerable expense.

Accordingly, replaceable cutting inserts are frequently mounted on toolbodies in such a manner that the inserts are readily replaceable, andare so disposed along the teeth of the cutting tool that they comprisethe cutting edges of the teeth. In this way, the cutting tool may becomposed of a lesser quality steel, and only the cutting inserts may becomposed of hard wear resistant material, suitable for metal cuttingapplications, such as hardened tungsten carbide. The cost of the toolitself may therefore be reduced and if the cutting edge, or portions ofthe cutting edge of the tool becomes subject to damage or excessivewear, it is only necessary to replace the inserts, or some of theinserts, to restore the cutting edge. This can frequently beaccomplished with relative simplicity in a few minutes. Indeed, in manycases the cutting inserts are indexable, in the sense that they comprisetwo or more essentially identical cutting edges, and it is onlynecessary to remove the insert and rotate it to appropriately introducea new cutting edge into position in order to renew a damaged orexcessively worn cutting edge or a portion of the cutting edge.

SUMMARY OF THE INVENTION

The present invention relates to a novel cutting insert of the typedescribed and a novel cutting edge configuration formed by such insertswhich exhibit improved cutting performance and reduced powerrequirements.

In accordance with one aspect of the invention, a cutting insert for usein a rotary cutting tool having helically arranged teeth comprises a sixsided block having two major parallel thombold-shaped plane surfacesconstituting a seating face and a clearance face respectively, twoopposed minor side surfaces constituting cutting faces extending betweensaid seating and clearance faces, each said cutting face forming anacute angle with the clearance face, and forming a cutting edge alongthe intersection therewith, and two minor parallel plane end facesextending between said seating and clearance faces and said two cuttingfaces. Each cutting face is provided with a concave curvature centrallyof its major dimension, and convex curvature at each end of its majordimension to define a serpentine cutting face and cutting edge. Suchinserts, when disposed along the helically arranged teeth of a rotarycutting tool result in a cutting face or radial rake face having acontinuously variable positive radial rake angle, and a cutting edgewhich parallels the helical form of the teeth.

In a further aspect, the invention resides in a rotary cutting toolcomprising a cutting portion having a longitudinal axis and a pluralityof helically arranged teeth separated by helical gullets extending thelength of the cutting portion, with the leading edge of each toothcomprising a plurality of sockets containing cutting tool inserts of thetype described above. The sockets are of complementary shape to thecutting tool inserts, and are so disposed along each tooth edge that theinserts are arranged along the leading edge of each tooth, substantiallythe length thereof, with cutting edges in operable relationship thereto.The cutting edges of the inserts in each tooth form an interruptedcutting edge of serpentine configuration which generally parallels theleading edge of the tooth and exhibits a cutting face or radial rakeface having a continuously variable positive radial rake anglethroughout its length.

The cutting edge thus created by the array of such cutting insertsresults in the creation of discontinuous lens shaped chips from aworkpiece subjected to the action of the cutting tool, which chips arereadily removed from the work area. The continuously varying positiverake angle of the cutting edge so created results in increased cuttingefficiency and reduced power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate the invention:

FIG. 1 is a side view of a milling cutter with helically arranged teethand cutting inserts in accordance with the invention;

FIG. 2 is an end view of the cutting portion of the milling cutter ofFIG. 1;

FIG. 3 is a perspective view of a cutting insert in accordance with theinvention;

FIG. 4 is a top plan view of the cutting insert of FIG. 3;

FIG. 5 is a cross-section of the cutting insert of FIG. 4 along lineV--V;

FIG. 6 is a side view of the cutting insert of FIG. 4 in the directionof arrow R;

FIG. 7 is a top view of a segment of a tooth cutting edge illustratingthe pockets formed therein;

FIG. 8 is a front view of the tooth segment of FIG. 7;

FIG. 9 is a cross-section of the tooth segment of FIG. 7 along the lineIX--IX;

FIG. 10 is a top plan view of an end cutting insert for the millingcutter of FIG. 1;

FIG. 11 is a side view of the end cutting insert of FIG. 10 in adirection of arrow X;

FIG. 12 is a developed view of the cutting portion of the milling cutterof FIG. 1; and

FIG. 13 is a developed view of the cutting portion of a modified millingcutter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, the milling cutter is illustratedgenerally by the reference numeral 1, and comprises a shank portion 2,and a cylindrical cutting portion 3. The shank portion is conventional,and will not be described further herein. The cutting portion comprisesfour helically arranged teeth 5 separated by gullets 6. Typically thehelix angle is about 25°, but it may range between 5° and 60°. Disposedalong the leading edge of each tooth, substantially from the shank endto the free end of the cutting portion, are a plurality of cuttinginserts 20 of identical shape. Special end cutting inserts 40 areprovided to complete the cutting edge of those teeth in which an insert20 is not seated at the extreme free end thereof.

The individual inserts 20 are best depicted in FIGS. 3 through 6. Eachof the inserts 20 comprises a relatively thin six sided block having anupper planar clearance face 21 which is generally rhomboid-shaped, and alower planar seating face 22 which is also generally rhomboid-shaped.The insert has two minor planar end faces 24, and two minor sidesurfaces 30. The side surfaces comprise cutting faces of the insert andeach forms an acute angle A (as shown in FIG. 5) with the plane of theclearance face 21. Typically the angle A is 20°, although it may varywidely depending upon the desired rake angle of the cutting edge formedby the insert. The inserts themselves are about 16 mm long, about 11 mmwide and about 5 mm thick, although, of course, these dimensions mayvary widely.

The cutting faces 30 are essentially identical. As best illustrated inFIG. 4, the cutting faces exhibit a concave curvature of radius Rcentrally of their major dimension, and a convex curvature of radius rat each end thereof. For purposes of illustration, the radius R may be50 mm and the radius r 30 mm. The intersection of the cutting faces 30with the clearance face 21 forms two cutting edges 32, and, as a resultof the aforementioned geometry, the cutting edges 32 are ofsubstantially identical serpentine configuration, and result in acutting face or radial rake face which exhibits a continuously variablepositive radial rake angle B from end to end, when operably mounted in acutting tool as will be described below.

In a conventional manner, the clearance face is relieved slightly,(typically at an angle of about 6°) to form a relatively narrow landsurface 31 at each cutting edge. The clearance face and the seating faceare chamfered at 35 and 25 respectively to avoid unnecessary sharp edgesand corners, and thus minimize the likelihood of chipping or breakage.

For the purpose of connecting the insert to the tool body, the insert isprovided with a through bore 28. This is conventional and is typical ofthe means of attaching cutting inserts to tool bodies, with the resultthat it need not be described in further detail.

As will be seen from FIGS. 1 and 2, the inserts are disposed along thecutting edge of each tooth and in generally complementary shapedsockets. The sockets are depicted in greater detail in FIGS. 7, 8 and 9.Socket ends 24' are complementary with ends 24 of the cutting insert,and an inboard side 30' forms an acute angle A with the upper surface ofthe tooth and exhibits a convex curvature R centrally of its majordimension, and concave curvature r at each end thereof. The angles,radius and dimensions of the socket are generally the same as thecorresponding angles, radius and dimensions of an insert but the socketis so dimensioned as to snuggly receive an insert therein. The base 22'of each socket has disposed therein a threaded blind hole 28' which isaligned with the through hole 28 of the cutting insert and whichcooperates with a threaded screw (not specifically illustrated) tooperatively secure the insert in the socket to the cutting portion ofthe cutting tool in a conventional manner.

As is best illustrated in FIG. 8, the base 22' of the socket slopes downslightly at an angle C of about 6° toward the free end of the cuttingportion of the tool so that the insert 30, depicted in dotted lines inFIGS. 8 and 9, projects slightly above the outer face of the cuttingportion at the end of the socket remote from the free end of the cuttingportion to substantially flush with the outer surface of the cuttingportion at the end of the socket closest to the free end of the cuttingportion. This slope is designed to maintain the top of the cutting edgeparallel with respect to the longitudinal axis of the tool. The slopewill vary depending upon the length of the inserts and the helix angleof the teeth. Further, that portion of the gullet 6 which forms theleading edge of each tooth 5 as illustrated in the FIG. 1 is in generalalignment with the cutting or rake face 30 of the insert as depicted inFIGS. 1 and 9.

As depicted in FIG. 1, and the developed view thereof in FIG. 12, thecutting inserts are so arranged along the teeth 5 that inserts inadjacent teeth are axially displaced so that an insert on one tooth willbe disposed midway between the transverse central planes P of adjacentinserts of an adjacent tooth. As a result, if the inserts are soarranged on some teeth, such as the second and fourth tooth illustratedin FIG. 12, that the tooth terminates at its free end with the end of acomplete insert, there will be a gap at the end of the adjacent teeth,for example the first and third teeth. Accordingly, provision is madefor attachment of a short end cutting insert at the end of each suchtooth in order to provide a cutting edge along each tooth which extendssubstantially to the free end of the cutting portion of the tool. Suchan insert 40 is depicted in FIGS. 10 and 11.

The end inserts 40 are conventional and need not be described in detail.They comprise a substantially planar outer or clearance face 41 which isgenerally rhomboid-shaped, and a substantially planar seating face 42which is also substantially rhomboid-shaped. The end cutting inserts 40also comprise substantially planar minor end faces 43 and substantiallyplanar minor side faces 44. The end faces 43 are relieved slightly at 45and form, at the intersection with side face 44 in the relieved area, acutting edge 46. The clearance face 41 is chamfered at 47 in aconventional manner to eliminate sharp edges and corners susceptible tochipping or breakage. A through hole 48 is provided in a conventionalmanner for attachment of the end insert to the free end of the cuttingportion of the milling cutter as depicted in FIG. 2.

As will appear from FIG. 1 and FIG. 12, the inserts are so arrangedalong each tooth as to form a generally serpentine cutting edge whichgenerally parallels the helical path of the leading edge of the tooth,and is interrupted by the gaps between adjacent sockets which, in thisparticular embodiment, are spaced apart slightly as illustrated in FIG.1, and in greater detail in FIGS. 7 and 8. The cutting edge of eachtooth as defined by the cutting edges of the inserts arranged along theleading edge of the tooth exhibits a continuously variable positive rakeangle as result of the tooth and insert geometry, i.e., the combinedeffect of the helix angle of the teeth and the serpentine rake face andcutting edge arising from the convex curvature of the rake face at eachend of each insert, and the concave curvature of the rake face of eachinsert centrally of its major dimension results in the continuouslyvariable positive radial rake angle. This form of insert, and thearrangement of the inserts along the leading edge of each tooth differsfrom any insert and arrangement of inserts of which applicant is aware,in that the cutting face and cutting edge of each tooth, as created byits inserts, follows the helical path of the leading edge of each tooth,and gives rise to a serpentine rake face and cutting edge which exhibitsa continuously varying radial rake angle along the length of the cuttingedge of each tooth.

As is best seen in FIG. 12, the inserts of one tooth are axiallydisplaced relative to the inserts of an adjacent tooth so that, in aplane transverse to the longitudinal axis of the cutting portion of thetooth, the concave curvature of the cutting face of one insert willoverlap the convex curvatures of the cutting faces of adjacent insertsin an adjacent tooth. In this way the gaps between inserts on one toothare covered by an insert on an adjacent tooth to produce a continuouseffective cutting edge.

An arrangement has been depicted in FIGS. 1 through 12 in which theinsert sockets are spaced one from the other in a regular spacing. It isalso possible to arrange the inserts so that their minor end faces 24abut, leaving no distinct spacing between the inserts. A developed viewof such an arrangement is depicted in FIG. 13, and it will be readilyseen that this arrangement results in a substantially continuous rakeface and cutting edge which follows the helical path of each tooth.There are however slight interruptions in the cutting edge, which resultfrom the chamfers 35, as depicted for example in FIG. 6, which result inthe formation of a slight chip breaker gaps in the cutting edges. Thesegaps, which are more pronounced in the embodiment depicted in the FIGS.1 to 12, result in the formation of discontinuous chips which are morereadily removed from the work area.

It is, of course, to be understood that the present invention is, by nomeans, limited to the particular construction shown in the drawing, butalso comprises any modifications within the scope of the appendedclaims. It will be appreciated that the cutting tools may varyconsiderably in diameter and size, and that the helix angle of theflutes as well as the rake angles, the number of teeth, etc. may alsovary. It is well known in the construction of cutting tools that suchaspects of the tools may also vary depending upon the cutting effectdesired.

I claim:
 1. A cutting insert for use in a rotary cutting tool havinghelically arranged teeth, comprising, a six sided block having alongitudinal axis and two major parallel rhomboid-shaped plane surfacesconstituting a seating face and a clearance face respectively, twoopposed minor side surfaces constituting cutting faces extendingparallel to said longitudinal axis and extending between said seatingand clearance faces, each said cutting face forming an acute angle withsaid clearance face and forming a cutting edge along the intersectiontherewith, and two minor parallel plane end faces extending between saidseating and clearance faces and said two cutting faces; each saidcutting face having a concave curvature centrally of its majordimension, and convex curvature at each end of its major dimension todefine a serpentine cutting face and cutting edge.
 2. A cutting insertas defined in claim 1 wherein each cutting edge is substantiallyidentically configured.
 3. A cutting insert as defined in claim 2wherein the radius of said concave curvature is greater than the radiusof said convex curvature.
 4. A cutting insert as defined in claim 3wherein the radius of said concave curvature is approximately double theradius of said convex curvature.
 5. A cutting insert as claimed in claim3 wherein said seating and clearance faces are chamfered along theintersection with said end faces.
 6. A cutting insert as claimed inclaim 5 wherein said clearance face is relieved adjacent each cuttingface to form a relatively narrow land surface along each cutting edge.7. A cutting insert as defined in claim 6 including means for securingsaid cutting insert to a rotary cutting tool body.
 8. A cutting insertas defined in claim 7 wherein said means for securing said insert to arotary cutting tool body comprises a through hole perpendicular to saidclearance and seating faces and disposed centrally thereof whereby saidcutting insert may be indexed by rotation about the axis of the throughhole.
 9. A cutting insert as defined in claim 6, wherein said acuteangle is about 20° the radius of said concave curvature is about 50 mmand the radius of said convex curvature is about 30 mm.
 10. A rotarycutting tool comprising a cutting portion having a longitudinal axis anda plurality of helically arranged teeth separated by helical gulletsextending the length of said cutting portion, the leading edge of eachtooth comprising a plurality of sockets and cutting inserts disposed insaid sockets, each cutting insert comprising a six sided block having alongitudinal axis and two major parallel rhomboid-shaped plane surfacesconstituting a seating face and a clearance face respectively, twoopposed minor side surfaces constituting cutting faces extendingparallel to said longitudinal axis and extending between said seatingand clearance faces, each said cutting face forming an acute angle withsaid clearance face and forming a cutting edge along the intersectiontherewith, and two minor parallel plane and faces extending betweenseating and clearance faces and said two cutting faces, each saidcutting face having a concave curvature centrally of its majordimension, and convex curvature at each end of its major dimension todefine a serpenting cutting face and cutting edge; said sockets being ofcomplementary shape to said cutting inserts and so disposed along eachtooth that said cutting inserts are arranged along the leading edge ofeach tooth substantially the length thereof, with cutting edges inoperable relationship thereto and in substantially parallel relationshipwith the leading edge of said tooth.
 11. A rotary cutting tool asdefined in claim 10 wherein said cutting portion is cylindrical andwherein the cutting edge along each tooth formed by said inserts is ofserpentine configuration and exhibits a continuously variable positiveradial rake angle.
 12. A rotary cutting tool as defined in claim 11wherein the helix angle of said teeth with respect to the longitudinalaxis of said cutting portion falls within the range 5° to 60°.
 13. Arotary cutting tool as defined in claim 12 wherein said helix angle is25°.
 14. A rotary cutting tool as defined in claim 11 wherein inserts onone tooth are displaced axially with respect to the inserts of theadjacent tooth whereby a concave curvature of an insert on one toothoverlaps the convex curvatures of adjacent inserts on an adjacent toothin a plane through said inserts transverse to the longitudinal axis ofsaid cutting portion.
 15. A rotary cutting tool as defined in claim 14wherein said inserts are arranged along said teeth in abuttingrelationship.
 16. A rotary cutting tool as defined in claim 14 whereinsaid inserts are arranged along said teeth in regularly spacedrelationship.
 17. A rotary cutting tool as defined in claim 15 whereinsaid cutting edges are interrupted between adjacent cutting inserts. 18.A rotary cutting tool as defined in claim 16 wherein said cutting edgesare interrupted between adjacent cutting inserts.